Lac repressor interference(Lac Switch)

Marcelo m.n.rivolta at
Wed Apr 22 03:13:18 EST 1998

Hi everyone!
I've been transfecting some new cell lines we have generated in the lab
with the lacI expressing vector (p3'SS) from the LacSwitch system
(Stratagene). The goal was to create a suitable cellular background to
use for further conditional expression studies with different genes.
However, the lacI itself seems to be altering the phenotype of these
cells, affecting the expression of a particular endogenous marker. The
expression of this marker is blocked when the lacI is on, and comes up
again when I perform the induction with IPTG. The technical people at
Stratagene never hear of such a thing.It is unlikely to be an isolated
problem because different clones from two unreated cell lines behave in
the same way.  My only explanation is that the promoter region of this
particular marker could be similar to the binding site of lacI, but of
course I can't check that out because we have no information on this
gene regulatory sequences. Has anyone ever seen this interference of
lacI with endogenous mammalian genes?
Any comments will be greatly appreciated
With thanks

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